The product of the herpes simplex virus type 1 (HSV-1) UL49 gene, the structural protein VP22 (4), is a major component of the HSV tegument, a compartment of the virion located outside the capsid and inside the envelope and composed of at least 10 or more additional virus polypeptides (for a review see (6)). VP22 has a molecular weight of 32 k, is very basic and is modified by phosphorylation and nucleotidylation (1,4,8,9,11) in the infected cell.
Despite being one of the major tegument proteins within the virion, together with the well characterised transcription regulatory protein VP16, little is known about the function of VP22 during the virus replicative cycle. It is not yet known if it is an essential virus protein, but it is possible that, in a manner similar to VP16, VP22 has two roles to perform during infection--initially as a functional protein during viral gene expression, and subsequently as a structural component of the virion during virus assembly. With regard to the former, some evidence exists to suggest that VP22 can bind specifically to HSV-1 DNA (2,8,10).